This invention relates to the field of human to machine interfacing and to helmet apparatus for conveying optical information to the crew of an aircraft. The invention also relates to a use of crew member head movements for selection of this optical information presented to the crew member.
The Head-Up Display (HUD) has become popular as a means for conveying information to the pilot or other crew member of a modern day aircraft. The head-up display usually involves the projection of optical images such as aircraft performance measurements, tactical information, and environmental sensing system outputs on the windshield or other screen like structure disposed in the normal vision line of the crew member. In addition to providing the display capability for relatively large quantities of information, the HUD provides for simultaneous viewing of displayed data and visual sight information, and other advantages over the previously used displays in an aircraft.
A primary limitation in the HUD, however, is that it is not slaved to the pilot's head movement and, therefore, if the pilot is looking outside of the field of view of the HUD, the information becomes unavailable. As a matter of practice the field of view range for HUD devices extends from about twenty to twenty-eight degrees, a field which is readily exceeded by crew members meeting the demands of a modern aircraft and its military mission
A desirable alternate to the HUD is found in the Helmet Mounted Display (HMD) wherein a crew member can, for example, look more than 90 degrees in the up, down, right, or left directions or rotate around the roll axis while retaining visual contact with the video image displayed by the helmet system. A HMD may employ one or a plurality of small screens which are attached to the helmet or goggles or other flight gear worn by the aircrew member and also includes an optical system arranged to present suitably projected images before of the eyes of the crewmembers. In addition to aircraft performance monitoring information and other flight symbology data, these images may include weapons systems information, and the environmental related images resulting from a radar system, an infrared transducer, or a visual light camera system, for examples. Such images are referred to herein by the generic term "flight video images".
When images of these types are presented to a crew member, however, it is often desirable to change the image that is presented in response to a change in the crew member's looking direction or sometimes even in response to his or her sitting posture. Clearly, for example, it is undesirable to present a continuous forward looking HMD image when the crew member is concerned with a threat or target situation appearing on the right or left. Indeed it is found that optimally most of the images displayed with a HMD system should vary with head position of the crew member. In such HMD systems therefore a means for continuously tracking the head position of the crew member is required.
It is significant to realize however that sensing the head position of an aircraft crew member and changing the HMD information according to this head positioning inherently involves time delays in presenting the updated flight video image. Since delays of this type are extremely objectionable and frequently result in disorientation and other human factors problems yielding degraded combat performance, it is found in practice that the reduction of such delays to times that are as small as possible and in any event not greater than 50 milliseconds is a desirable performance criteria for a useful HMD system. In many present day attempts to use HMD systems it is found for example that delays between 66 milliseconds and 73 milliseconds are encountered. Such delays can be very disconcerting at the least, in the aiming of a weapons system, for example. The reduction of such delays to more acceptable values is a principal motivation supporting the present invention.
According to the present invention, therefore, an improved arrangement for generating the signal representing crew member head position is achieved. For the sake of convenience in describing the invention azimuth related signals as developed by a magnetic head positioning apparatus will be principally described. Extension of the disclosed predictive tracking technique to a combined elevation and azimuth and roll and crewmember posture responsive system can, of course, be accomplished by persons skilled in the art in view of the disclosure herein.
The prior patent art includes several examples of inventions which relate to certain limited portions of the present invention; included in this prior patent art is the U.S. Pat. No. 4,156,292 of D. P. Helm et al which involves a display carrying protective helmet for crew members; the Helm et al invention is, however, concerned with details of the helmet and optical portions of the display system.
Also included is the patent of Edwin Cohen, U.S. Pat. No. 4,181,405, in which a viewed image is presented on the Helmet visor used by an aircrew member. The Cohen apparatus is principally concerned with the optical and other general properties of the display system.
Also included is the patent of J. A. Aileo, U.S. Pat. No. 4,231,117, which is concerned with physical positioning of a visual display unit with respect to the shell of a helmet worn by a viewer and with details of the helmet structure. The Leo patent is not, however, concerned with the sensing of movement and positions of the wearer's head.
Also included in these prior patents is the patent of P. F. Tasler et al, U.S. Pat. No. 4,259,747, which is concerned with physical details of a helmet providing a combination of visual and audio communication as well as physical protection for the wearer. The Tasler et al patent is also concerned with physical details of the helmet and its appearance as opposed to sensing the head positioning of the helmet wearer.
None of these prior patents therefore is concerned with the generation of helmet position indicating signals or with elimination of the delay between movement of an aircraft crew members head and changes in the information presented on a HMD apparatus.